The conventional evaporative cooler constantly replenishes water from a water supply when in operation, through a float valve in the sump, to make up for water loss due to evaporation in the airstream. The incoming water always contains a small concentration of salt dissolved in it. If no means are provided to remove that salt, it will concentrate in the sump of the cooler, since only pure water is evaporated into the airstream.
Concentration of salt, if allowed to become too high, has several detrimental effects including:
a) crusting of the salt on pads, lowering their effectiveness and decreasing their life; PA1 b) decreasing the performance of the cooler by reducing evaporation rate; PA1 c) providing tracking paths which enable leakage from the cooler to take place; and PA1 d) increasing corrosion rate on the vulnerable components which are subject to corrosion.
These problems have been well recognised and traditional methods of controlling salt concentration include allowing bleeding of the water, or periodically actuating a dump valve to dump the tank or sump to drain. However these methods drain much more water to the drain than is actually required for salt control, thereby wasting water and adding to the operating cost of the cooler. This is a matter of considerable importance in arid areas where water is scarce.
The most relevant art otherwise known to the Applicant is disclosed in a brochure produced by Munters (Aust) Pty Ltd, of Cheltenham, Victoria, Australia, which discloses a conductivity controller in an evaporative cooling system wherein conductivity (a function of total dissolved solids) is continuously measured, and upon passing a set point, opens a solenoid valve and bleeds off system water until it is back within control range. Although the concept is simple, the structural features of such an arrangement discloses three valves in addition to a solenoid valve in a bleed line, and a separate by pass sample line which includes a conductivity probe assembly.
One object of this invention therefore is to provide a mechanically simple device which will effectively bleed off sump water from a cooling system to maintain an acceptably low salinity within the sump, and this is achieved primarily by use of resistance sensing probes which, upon salinity increase, initiate a timer which operates a solenoid valve to effect bleed-off, without interrupting cooler operation.